You can also make kefir, that's what
I do--it has many more live cultures than yogurt, and you can
make a gallon at a time and keep it in the fridge in a milk carton
if you feed it every day, as I do. That way you can also control
what kind of milk it is made with (whole, skim, goat, organic,
etc.)
I buy kefir starter from Karidan's. Once you make the first batch,
you can start the next batch from the remnants of the first,
without starting over, for up to a month or so. Very economical.
Today was my dogs' "fasting day", so they just had
kefir and honey for dinner, nothing else. Honey is also a digestive
tonic.

First, buy a kefir starter. I get mine
from Karidan's (888) 697-9374, though I am sure many health-food
stores might carry it. Then, choose your milk. Goat's milk is
easier to digest for dogs, but cow's milk is fine when cultured,
so that's what I use. It's also more economical, especially when
you have 5 dogs on Natural Diet. I use whole milk, because my
guys are high-energy, and it seems I'm always having to pack
in the calories. You can use 2% or skim, too, doesn't matter.
Anyway, it's very simple:

First, heat the milk to 180 degrees,
or to the boiling *point* (don't let it boil). Then, let it cool.
This takes a while. When the temperature gets down to 70 degrees,
add the starter, or "culture". Mix well until dissolved,
and pour back into the gallon (or half-gallon, whatever) container.
Then, and this goes against everything you've ever been taught
about milk, you LEAVE THE CULTURED MILK OUT--that's right, just
out on the counter at room temperature--for 24 hours or so, until
curds start to form. The longer you let it culture, the thicker
and "lumpier" it will get, though you can shake it
up to break the lumps. Kefir should always smell fresh, but cultured--like
yogurt or sour cream, it should never smell "spoiled".
When
the milk is properly cultured, put it in the refrigerator for
at least 8 hours to stop the growth of the culture. For storage,
I always just pour the kefir back into the milk carton--easy
as can be, much simpler than making yogurt, IMO.

NOW, and this is the beauty part, to
me--when you get down to the last cup or so of kefir, just get
a new gallon of milk, pour out a cup, and add the last cup of
the kefir. Leave the new gallon sitting out overnight, and *presto*!
A fresh batch of kefir! This can be repeated as many times as
necessary,
for about a month, before you need to start over with a new packet
of starter and go through the heating/cooling process again.

Kefir has many more live cultures than
yogurt, and although I try to stay away from dairy (I have endometriosis),
I see ads in Natural Health magazine all the time claiming its
health benefits for people. They sell it in health food stores
in a carton like milk, it is a drink for people. The dogs seem
to like it a little thicker, like yogurt. On fasting days, my
dogs(about 50
lbs.) get a cup of kefir with 2 tablespoons of honey, as a digestive
tonic. This is a great cleansing regimen for them. Otherwise,
they get 1/2 cup of kefir every day as part of the Volhard Natural
Diet (uses bone meal, not bones, so don't anyone get all upset
about the diet, please). The fosters
and rescues who are temporary and don't get put on Natural Diet
still get kefir with their kibble every day, and I think it helps
them digest the kibble better.